Pre-heat oven to 220°C/425°F. Halve Brussels sprouts. Evenly spread walnuts and halved Brussels sprouts on a baking sheet. Drizzle with part of the olive oil and generously season. Roast for approx. 20 min., tossing once after half of the time is up.
Meanwhile, bring water to a boil and add couscous. Stir well, remove from heat, and cover the saucepan. Let sit for approx. 5 min. while covered. Remove lid and fluff with fork. (It is important to remove lid so that couscous does not become gummy.)
Dice bell pepper, shallot, and tomatoes. In a frying pan, heat part of the olive oil. Then, add bell pepper and shallot and fry until slightly browned.
Add tomatoes and fry until they are softened and their juices begin to release.
Add balsamic vinegar to coat the vegetables.
Add roasted walnuts and Brussels sprouts and continue to toss until balsamic vinegar has become slightly caramelized.
Add couscous and mix well. Add the remaining olive oil and season with salt and pepper.